by Doug Stanglin, USA TODAY

by Doug Stanglin, USA TODAY

On the 17th day of his sensational murder trial, Olympic sprinter Oscar Pistorius finally took the stand Monday and began by apologizing to the family of Reeva Steenkamp, the girlfriend he fatally shot during what prosecutors say was an argument.

Pistorius maintains that he shot the 29-year-old model accidentally when he fired four shots through a locked bathroom door at what he thought was an intruder.

"There hasn't been a moment since this tragedy happened that I haven't thought about your family," the double-amputee runner said at the trial in Pretoria, South Africa. "I wake up every morning and you're the first people I think of, the first people I pray for."

Pistorius testified that he takes anti-depressants and sometimes wakes up in terror and suffering from panic attacks. He told the court that he thought someone had broken into his apartment when he fired the fatal shots on Valentine's Day last year.

"I was simply trying to protect Reeva," he said.

"A security guard stands outside my door at night," he said. "I wake up in a state of complete terror at the slightest noises."

Pistorius, who has been described by prosecution witnesses as obsessed with guns, said he never wants to handle a firearm again, Times Live reports.

His mother, he said, also had security concerns and "kept a firearm in a padded bag under her pillow." Pistorius said his mother was concerned about crime, particularly since his father was often not around.

"She often got scared at night. We didn't live in the best of areas. There was a lot of crime. She would call the police, call us to her room and we would wait for the police to arrive," he testified.

In addition to the murder charge, Pistorius is also charged with violating the Firearms Control Act. One prosecution witness testified that Pistorius once fire his pistol through the sunroof of his car after an altercation with police.

He faces 25 years to life in prison if convicted of that charge.

The court allowed for an early adjournment for the day after the defense attorney said Pistorius was exhausted.

Asked about his state of mind on the stand, Pistorius said, "I am just tired. This is a lot of things going through my mind and the weight is extremely overbearing. It is just a lot of think about."

During his testimony, the runner talked about his experiences growing up disabled, saying his mother taught him to stand up to bullies and not let anything hold him back. Pistorius said he has tried to share that outlook with others, once hosting a race in a town in Mozambique as part of his work with landmine victims.

He said he had challenged anyone in the town to step forward and run against him. He said he beat them all, giving many who had been injured new confidence.

Before Pistorius' dramatic testimony, his defense called a pathologist in an effort to cast doubt on the prosecution's assertion that Steenkamp ate no more than two hours before Pistorius shot her.

The testimony by Jan Botha was critical to the defense because Pistorius has claimed the couple was in his bedroom by 10 p.m. on Feb. 13, 2013, and any indication that the two were awake much later could undermine the Olympian's account of the sequence of events.

Botha said the time frame of digestion was difficult to assess because of variations in many factors, including the volume of food consumed, its caloric content and the psychology of the person who was eating. The testimony countered statements by a pathologist called by the prosecution who said that, judging by the food contents in her stomach, Steenkamp probably last ate no more than two hours before her death.